The growing production of biofuel, particularly of biodiesel, as alternative to the use of petrol based biofuels is based in two basic needs of the socioeconomic model in the industrialised countries. On one hand, the reduction of the petrol dependency whose prize has been significantly increased during the last years and with a predicted growing tendency. On the other hand, the reduction of emissions associated with the diesel combustion in vehicles engines, with special emphasis in CO, CO2, SOx and particles, which has been proved to be reduced in the case of biodiesel use, although the NOx level are still high.
The current biodiesel process is based in a transesterification of vegetable and based triglycerides with methanol or ethanol to obtain fatty acid methyl or ethyl esters (biodiesel) and glycerol (concomitant byproduct in the transesterification reaction) obtaining approximately 100 tones of glycerol pre 1.000 tones of biodiesel. If in 2005 the European objectives of the substitution of 2% of petrol based diesel for biodiesel were accomplished, Europe would have been produced 400.000 tones of glycerol per year, that is, approximately double the needs of the current European glycerol market. This high annual production of glycerol represents one of the most important inconveniences in the biodiesel manufacture, which could affect negatively in the development of the biodiesel market.
It is necessary, therefore, to develop new high market application for the produced glycerol in the biodiesel manufacturing. It has been recently proposed a cheap transformation of glycerol in substances to be mixed with alkyl fatty acid esters ready to act as a biofuel. This solution could be of high technical and commercial value and it will solve the problems derived from the excess of glycerol.
For example, the patent filed WO 2005/093015 A1 described the preparation of two glycerol acetals through the reaction of glycerol and n-butanal and acetone. It is also described the preparation of glycerol t-butylethers through the reaction of crude glycerol and isobutylene. In both cases the glycerol used was crude glycerol as byproduct in the biodiesel manufacturing from the transesterification process of rapeseed oil with methanol in the presence of zinc aluminate as a heterogeneous catalyst. It is reported that both ethers and acetals described are mixed in an 80/20 p/p (biodiesel/glycerol derivative), ensuring, then, the total utilisation of glycerol as biofuel. However, the low temperature miscibility is not reported, therefore, is not possible to evaluate the behaviour as biofuel at low temperature, an important aspect to determine the general use of biofuels in cold climates.
The European patent filed EP 1331260 A2 described a procedure to produce biodiesel fuels with improved properties at low temperature. In this case the crude glycerol obtained in the preparation of biodiesel is reacted, after its neutralisation with H2SO4 to pH 7, with aldehydes and ketones through known procedures to obtain acetals and ketals. The properties at low temperature of methyl esters of rapeseed oil and glycerol formal and with glycerol triacetate is described in weight proportions from 95.5/0.5 to 90/10 (biodiesel/glycerol derivative). The data reported showed that the addition of glycerol formal derivative into the biodiesel produced a maximum freeze point reduction (−21° C.) and of viscosity at −10° C. (343.3 cST of a 95/5 mixture). In the light of this result it seems that glycerol formal constitute one of the most efficient alternative to warrantee the best properties of biodiesel at low temperature. Although the author indicates that the concentration of acetals, ketals and glycerol acetate may vary between 0.1 and 20% weight depending of the needs, it is not indicated is it is possible to prepared mixtures of glycerol formal and biodiesel when the amount of glycerol formal is high of 5%. The data obtain in our laboratory shows that the glycerol formal is immiscible with fatty acid based methyl esters derived from vegetable oils such as rapeseed, sunflower or palm oil, when the proportion of glycerol formal is 20% at the temperatures ranges between −20 and +25° C., excluding, then, glycerol formal as a component of biodiesel fuel formulation, allowing the complete incorporation of glycerol.
On the other hand, the literature studied (e.g. the article “Glycerinderivate als Kraftstoffkomponenten”, R. Wessendorf, Erdöl und Kohle-Erdgas, 48, 3, 1995) does not contemplate the associated cost in the use of aldehydes, ketones, olefins and other chemical products needed for the synthesis of the proposed glycerol derivatives. Form the economical point of view, glycerol formal is a suitable material for the preparation of biofuel since its industrial availability and its prize may be competitive enough.
Finally, from the strategic point of view it is convenient to base the chemical production in Europe in the use of renewable materials or from natural gas, minimising the use of petrol derivatives (Strategic Research Agenda. Technology Platform of Sustainable Chemistry). This vision is not only to be taking into account in the production of biofuels only but also is adopted as a general directive. With all this data on hand, is it possible to conclude that glycerol formal is the most suitable glycerol derivative since the starting material needed for its production, formaldehyde, is prepared from methanol, which is obtained from the oxidation of natural gas.